Observation of the Transport and Removal of Lipofuscin from the Mouse Myocardium using Transmission Electron Microscope

Abstract

This study was performed to investigate whether the lipofuscin formed within cardiomyocytes can be excluded by the myocardial tissue. We have provided indicators that can be used for future studies on anti-aging interventions.In the present study, the heart of a 5-month-old BALB/c mouse was obtained for resin embedding and ultra-thin sectioning. The specimens were observed under a Hitach 7500 transmission electron microscope, and the images were acquired using an XR401 side-insertion device.Lipofuscin granules are found abundantly in myocardial cells. Cardiomyocytes can excrete lipofuscin granules into the myocardial interstitium using capsule-like protrusions that are formed on the sarcolemma. These granules enter the myocardial interstitium and can be de-aggregated to form “membrane-like garbage”, which can pass from the myocardial stroma into the lumen of the vessel through its walls in the form of soluble fine particles through diffusion or endocytosis of capillaries. Smaller lipofuscin granules can pass through the walls of the vessels and enter the blood vessel lumen through the active transport function of the capillary endothelial cells. When the extended cytoplasmic end of macrophages and fibroblasts fuse with the endothelial cells, the lipofuscin granules or clumps found in the cells of the myocardial interstitium are transported to the capillary walls, and then, they are released into the lumen of the blood vessel by the endothelial cells.The myocardial tissues of mice have the ability to eliminate the lipofuscin produced in the cardiomyocytes into the myocardial blood circulation. Although there are several mechanisms through which the myocardial tissues release lipofuscin into the bloodstream, it is mainly carried out in the form of small, fine, soluble, continuous transport.

Redox changes in obesity, metabolic syndrome, and diabetes

“…Extraneuronal lipofuscin was found in the brain samples, suggesting a possible physiological removal from the nerve cells to the capillary endothelium and its later elimination via phagocytosis by glia cells [ 127 ]. Indeed, recent findings have shown that lipofuscin could be exocytosed from the cardiomyocytes into circulation through capillary endothelium [ 128 ]. Hence, lipofuscin could be regarded as a promising redox biomarker of obesity and diabetes.…”

Mini-Review on Lipofuscin and Aging: Focusing on The Molecular Interface, The Biological Recycling Mechanism, Oxidative Stress, and The Gut-Brain Axis Functionality

“…It has been also documented on rats that zinc deficiency promoted an accumulation of waste-trash products retinal pigment epithelium (RPE), concomitantly with lipofuscin-loaded macrophages in the choroids followed by the presence of such cells at Bruch’s membrane [ 16 ]. While Julien revealed that a zinc-based diet could exert beneficial effects on adult Long Evans (LE) rats, it was demonstrated this year, by Wang et al [ 17 ], through transmission electron microscope, that myocardial tissues of mice possess the ability to eliminate unnecessary bio-products into the associated bloodstream.…”